Tile aim of the Cell and Tissue Evaluation Core is to provide a broad spectrum of techniques and assays for examining photosensitizer levels and localization in cells and tissues and the changes induced by different photodynamic therapy (PDT) regimes, as required by the individual Programs in the Program Project. The support offered is based on well-defined and established methods with proven utility. In addition existing methods will be modified or new methods will be developed to optimize tile information gained from shared samples. Services, assays, analyses and procedures will include: 1. Cellular and tissue distributions and subcellular localization of photosensitizers before and after irradiation, by fluorescence microscopy and confocal microscopy. 2. Drug levels in tissues, cells and biological fluids using absorbance and fluorescence directly and after extraction and/or solubilization. 3. Flow cytometry of surface and intracelhdar markers, physiological probes and cytokines and the response to PDT. 4. Analysis of cell death pathways (apoptosis and necrosis) by flow cytometry, fluorescence microscopy, caspase assays and Western blots. 5. Ligand binding studies to whole cells, mitochondria and/or other organelles. 6. Routine preparation of samples for histological and inmmnohistochemical staining. Development of additional staining methods as required. Tim Core personnel will supervise or perform the assays on samples generated by tile different Projects. The Core will focus on co-ordinating assays on the same samples to provide efficient data production and consistency, to maximize the information obtainable, and to facilitate the exchange and sharing of data.